Well, faster is always better,that being said 2ghz is still great for audio.
If it were me, I'd get the 2ghz, but then very shortly bump the RAM to 4GB and toss in an aftermarket 7200rpm drive, as both of those would make a bigger difference, imo.

Previous to my Thinkpad I had a 2ghz C2D HP business notebook, and my track count and VSTi count didn't dramatically increase going to the TP.

Also realize that with both Logic Pro and Logic Express, when you're proc runs out of steam you can "freeze" the tracks, effectively rendering them temporarily while disabling the applicable plug-ins to free up power.

I've gotten a ton of extra tracks this way in Tracktion, I'm sure it's just as effective in Logic.

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